ATLANTA | The Democratic challenger to Gov. Nathan Deal has pulled into the lead, according to a public-opinion survey released Thursday.

Jason Carter, a Democratic state senator from Atlanta and grandson of Georgia's only president, is slightly ahead of Deal, 41 percent to 38 percent.

However, the margin of error is 4 percent, leaving the two candidates effectively tied.

The online survey of 486 voters was conducted Sunday and Monday by InsiderAdvantage with OpinionSavvy on behalf of Morris News and WAGA-TV in Atlanta. It showed 21 percent remain undecided.

Fifty-nine percent of independents favor Carter, and more than one-fourth of Republicans haven't made up their minds. That could be because Deal must overcome two challengers from his own party in the May 20 primary before facing Carter and Libertarian Andrew Hunt in the November general election.

Carter said he has sensed momentum building.

"We feel like we're getting a huge response, but it's a long campaign," he said.

He didn't attribute the results to any single factor, such as Deal's handling of a January snow storm that left thousands of Atlanta motorists stranded in their cars for hours and children stuck overnight in schools.

"I don't know," he said. "The governor has a record that all of us know."

"I can tell you from internal numbers that we have done for other Republican House members, and Gov. Deal is doing just fine," he said.

McElhannon said his clients didn't want to release those results because of other questions in their polls. He also raised doubts about online survey techniques.

"On average, Carter’s name ID is very low, and he’s trailing Deal by large margins. To argue that now Georgians have had a double-digit reversal and that Carter has surged in name ID and support without doing any advertising defies conventional political wisdom," he said.

InsiderAdvantage CEO Matt Towery, a former GOP legislator and nominee for lieutenant governor in the 1990s, acknowledged Carter's lack of name identification and said that shows his support comes from people upset with the governor.

Towery also defended his polling methods, saying the online results were in line with other telephone surveys he has done recently.

"The last phone poll we had, Deal was losing to Carter by almost 10 points," he said.

Overall, Towery observed that neither candidate has done much advertising. Deal aired some ads touting job creation but discontinued those. Most strategists believe that the benefit of ads evaporates quickly after they stop running.